The present invention relates to curable coating compositions and to a method for producing curable gel-free coating compositions. More particularly the present invention relates to a gel-free silica acrylate curable coating composition.
Curable coating compositions based on silica acrylate resins are generally made using colloidal silica. It is desirable to produce a stripped coating by removing water from colloidal silica azeotropically, using a compatible solvent, for example isopropyl alcohol, and leaving the treated silica in a reactive acrylate carrier. It has been shown that when this reaction is run under a nitrogen atmosphere, a gel forms at a point during the stripping process when nearly all of the compatible solvent is removed. It is known that highly reactive acrylates require oxygen to prevent gelation, hence typically this stripping operation has been run under at least some oxygen. Due to the flammability of the compatible solvents, it is highly desirable to run these reactions without the addition of oxygen. Further, in the stripping vessels typically used, it is difficult to assure adequate oxygen dispersion. The method of the current invention, is a process for making gel-free curable coating compositions, without requiring the addition of oxygen to the system. Further, it has been found that coating compositions which are so stripped have exhibited longer shelf-lives.
The term "gel-free" refers to coating compositions in which viscosity is controlled within useful limits. The viscosity will of course vary depending on the specific polymers, however when the composition is diluted in a suitable solvent, essentially no undissolved material remains.
U.S. Pat. Nos. 4,486,504 and 4,455,205 relate to formulations of weatherable and non-weatherable UV curable hard coat compositions.
U.S. Pat. No. 4,973,612 to Cottington et al. relates to coating compositions which contain multifuntional acrylates, unsaturated organic compounds and aqueous dispersions of colloidal silica.
U.S. Pat. No. 4,644,077 to Gupta relates to a process for producing organophilic silica.
U.S. Pat. No. 4,491,508 to Olsen et al. relates to a method for making a solventless hard coat composition, which may be useful in the current invention.
U.S. Pat. No. 4,478,876 to Chung relates to a process of coating a substrate with an abrasion resistance ultraviolet curable composition. This process relates to forming the composition under a non-inert atmosphere such as air.
Generally, the above patents describe coatings which can be improved by use of the method of the current invention.
U.S. Pat. No. 5,120,811 to Glotfelter et al. relates to an organic/inorganic (epoxy/glass) wear surface coating over a clear, protective layer providing excellent stain and gloss protection. An acid hydrolyzed silicate is combined with an acid hydrolyzed silicone coupling agent, an epoxy monomer, a photoinitiator and silicon oil surfactant, but no colloidal silica or acrylate monomer is used.
U.S. Pat. No. 5,103,032 to Turner et al. relates to compositions containing an acryloxysilane or a methacryloxysilane and an N,N-dialkylaminomethylene phenol in an amount at least sufficient to inhibit polymerization of the silane during its formation, purification and storage, however, there is no mention of the use of colloidal silica.
U.S. Pat. No. 4,831,093 to Swarts relates to the polymerization of methyl methacrylate with initiator of perester salt of maleic acid using a bisulfite activator in water-in-oil emulsion, but does not contain SiO.sub.2.
U.S. Pat. No. 4,780,555 to Bank relates to a method for preparing acryl-functional halosilanes by reacting a halosilane with an acryloxy or methacryloxy-functional organic compound in the presence of a platinum hydrosilation catalyst and a stabilizing amount phenothiazine, wherein the reaction mixture is contacted with an oxygen-containing inert gas. No salt or surfactant is suggested for use as an compound.
U.S. Pat. No. 4,709,067 to Chu et al. relates to an improved process for preparing, purifying and/or storing methacryloxy or acryloxy containing organosilicon compounds without the undesirable polymerization normally associated with the methacrylate bonds. No salts or surfactants are suggested for inhibiting this polymerization, and the polymerization here is associated with methacrylate bonds.
U.S. Pat. No. 4,021,310 to Shimizu et al. relates to a method for inhibiting the polymerization of acrylic acid or acrylic esters during the distillation for separating or purifying the acrylic acid obtained by the vapor phase catalytic oxidation of propylene or acrolein, or the acrylic esters derived from said acrylic acid. There is no mention of colloidal silica, and the inhibited polymerization is that of acrylic acid or acrylic esters.
U.S. Pat. No. 3,258,477 to Plueddemann et al. relates to alkoxysilanes and compositions thereof, and fails to disclose the use of colloidal silica.